1. Field of the Invention
The invention relates to a distribution system for a local area network. The distribution system comprising a distribution unit which is coupled to a plurality of subscribers' premises via optical transmission links. The premises of each subscriber are provided with a common terminal unit having at least one input and a plurality of outputs, the input of the common terminal unit being coupled to an optical transmission link and the outputs being connected to a plurality of sockets via further transmission links.
2. Description of the Prior Art
In this specification a local network is intended to mean all transmission paths and equipment between a central unit and sockets provided at the premises of the subscriber. A distribution system of the type mentioned is disclosed in, for example, "Proceedings of the IEEE", volume 68, no. 10, October 1980, page 1295, FIG. 5. In the common terminal unit of this prior art distribution system the incoming optical signal is converted into an electrical signal, whereafter the electrical signal is applied to a demultiplexer. The outputs of the demultiplexer are connected via coaxial cables to the respective electric wall sockets in the subscriber's premises. The wall sockets are further connected via coaxial cables to the inputs of a multiplexer, the output of which is connected to an electro-optical converter. This combination is employed for the optical signal outgoing from the subscriber's premises to provide services, such as, for example, telephone, channel selection for television, alarm systems etc.
A disadvantage of this prior art system is the fact that the local network is not tolerant to future system changes and extensions, such as the choice of analog or digital signals, bandwidth, bit rate, number of services and connections per subscriber. When, for example, a new colour or a new service is added to the existing optical transmission system, it will be necessary to make changes in all the common terminal units in a local network. Multiplexers, demultiplexers, switching apparatus, etc. will have to be adapted to this new colour or service.
In addition, the known distribution system has the disadvantage that when common terminal unit equipment becomes defective for example the demultiplexer, this may cause all services, such as television, radio, telephone, etc. to disappear simultaneously. This can be prevented from occurring by providing duplicate equipment in the common terminal unit. As soon as one set of equipment present in the common terminal unit becomes defective, a switch to the relevant duplicate set of equipment is automatically made. An alarm may then, for example, be triggered simultaneously, so that the defective equipment can be replaced. This method has, however, the disadvantage that duplicate equipment must be provided for every piece of equipment present in the common terminal unit and additional switching equipment is also required. This means a considerable increase in the costs of the common terminal unit at each subscriber's premises.
The invention has for its object to provide a distribution system for a local area network, in which the above-mentioned disadvantages are reduced.